The present invention generally relates to gas turbine engine control, and in particular to fuel control systems and methods for gas turbine engines.
Gas turbine engines run on a number of different types of fuel gases including natural gas, LPG""s such as propane and butane, refinery gases, and coal-derived gases. Many engines are set up as dual fuel applications with a primary fuel source and a backup fuel source. Gas turbine engines, whether used on the ground for power generation, in flight for propulsion, or as a secondary power source, are typically controlled by an electronic control unit (hereinafter ECU). Control schedules and control logic for the engine are incorporated within the ECU. Electronic engine controls are designed based on the fuel type for that particular application. Because engines run on many different types of fuels, control schedules and logic have to be calculated for each fuel. Known within the art is the use of ECU""s to determine the appropriate fuel flow to the particular engine. However, this is generally cumbersome, not easily amenable to a multitude of different types of fuel, and requires customization for each type.
U.S. Pat. No. 3,875,380 issued to Rankin discloses an Industrial Gas Turbine Power Plant Control System and Method Implementing Improved Dual Fuel Scheduling Algorithm Permitting Automatic Fuel Transfer Under Load. The ""380 patent allows for computer control of fuel subsystems to achieve uninterrupted operation during transitions from operation on one fuel to operation on another or to operation on a mixture of the two fuels. This provides a system capable of operating with more than one fuel type. However, such systems generally require customization for each fuel type, and only allow for two fuel types.
U.S. Pat. No. 6,226,976 issued to Scott discloses a Variable Fuel Heating Value Adaptive Control For Gas Turbine Engines. The ""976 patent allows for a control and method that continuously adjust fuel sensitive schedules in the ECU for changes in the heating value of the fuel being combusted by the engine. This is accomplished by calculating an expected fuel flow for a baseline fuel type and an actual fuel flow. A ratio of these two fuel flows is determined and applied to the heating value of a baseline fuel type that is preprogrammed into the ECU. This results in a scale factor that is then applied to fuel sensitive schedules in the ECU. While the ""976 patent represents a significant advancement within the art, it applies specifically to a particular engine type, affects only part of the engine control logic, and is applicable to one engine subject to varying fuel types while running.
Accordingly, there is a need for a system and method that applies generally to all engine types, affects the entire fuel control system, and is applicable when several of the same engine models are used in applications with differing fuel types. There is also a need for a system and method that allows for control of fuel subsystems that run on a multitude of different fuel types and do not require customization for each fuel type.
In one aspect of the present invention, a method for adjusting the gains and schedules in an electronic control unit for a gas turbine engine comprises the steps of determining engine requirements and calculating a desired energy flow for at least one engine; maintaining desired engine conditions according to the desired energy flow; converting the desired energy flow into expected fuel flow according to the specific fuel being utilized; calculating a fuel flow command; and communicating the fuel flow command to at least one fuel valve.
In another aspect of the present invention, a method for adjusting the gains and schedules in an electronic control unit for a gas turbine engine comprises the steps of determining engine requirements for at least one engine and calculating the desired energy flow for each engine to be delivered to a gas turbine engine; maintaining desired engine conditions according to the desired energy flow; converting the desired energy flow into expected fuel flow according to the specific fuel being utilized, wherein at least two fuel types are being utilized; calculating a fuel flow command for the fuel types; determining a ratio according to the respective fuel types; applying the ratio to the fuel flow to determine a fuel flow command; and communicating the fuel flow commands to at least one fuel valve.
In a still further aspect of the present invention, a gas turbine engine comprises a compressor receiving ambient air, a combustor receiving compressed air from the compressor and fuel from a fuel nozzle, a turbine receiving combusted gas from the combustor and expelling the gas into an exhaust; a shaft coupling the compressor and the turbine, at least one fuel control unit, an electronic control unit electronically coupled to the engine and the fuel control unit, with the electronic control unit having at least one energy sensitive control schedule, and the electronic control unit determining a desired energy flow, maintaining desired engine conditions according to the energy flow, and converting the energy flow into at least one fuel flow command that executes a command to a fuel valve.